WASHINGTON (Reuters) - The U.S. State Department called on Iran on Monday to immediately release a South Korean-flagged tanker that it seized in the Gulf and accused Tehran of threatening freedom of navigation as a way to extract relief from economic sanctions. “The (Iranian) regime continues to threaten navigational rights and freedoms in the Persian Gulf as part of a clear attempt to extort the international community into relieving the pressure of sanctions. We join the Republic of Korea’s call for Iran to immediately release the tanker,” said a State Department spokesperson on condition that they not be identified.